The Flow-routing is improved and now allows the definition of RoutingParameters
via HTTP-components that can later on be handled by custom RoutePartHandlers.
That way the routing can react to influences other than the uri-path like the
requested host-name or scheme or any other computable value.

Attention: The signature of the internal Router implementation has changed.
In the unlikely case that you replaced the flow-router with a custom-router
you have to adjust your code accordingly.

Routing Parameters can be defined globally (via HTTP component) in order
to allow custom RoutePart handler to react to influences that are outside of
the incoming URI path (example: The requested host name or scheme)

For a RoutePart handler to access the parameters they have to implement
the new ParameterAwareRoutePartInterface.
The DynamicRoutePart already implements the interface. For custom implementations
extending DynamicRoutePart the parameters will be accessible via $this->parameters.

Currently the composer class loader is only used as a fallback to our own,
but especially if the optimized loader is used the composer one is much
faster.

On systems in which all packages/classes are registered correctly via
autoload statements in composer.json files using our own class loader
only for proxy classes can bring an substantial boost in performance for
every request.

In order to enable this feature you need to set an environment variable
FLOW_ONLY_COMPOSER_LOADER=1. Please test carefully if that breaks due
to your autoload configuration not being fully composer ready.

Additionally it is recommended to use the optimized composer loader by
calling composerdumpautoload-o.

While not breaking in itself this change deprecates using our class loader
for anything else than proxy classes. In practice this means you should
always enable composer auto loader only by using above mentioned environment
variable. At least make sure that your projects work with this
enabled.

We will drop the variable and make this the default behavior in the next
major version of Flow (version 5.0) which means only classes that are
correctly added to composer (loaded) packages with autoload configuration
are being loaded correctly.

The log-package was extracted from Flow to become a separate independent
composer-package neos/flow-log that can be used outside of Neos or Flow
projects. This continues our long-time-effort of extracting parts of our
odebase that can be used separately and making them available to the
whole php-community.

The SystemLoggerInterface and SecurityLoggerInterface are kept
in Flow as they have not much meaning in the Logger package. Additionally
the EarlyLogger was not moved as it depends on those interfaces.